This study aims to understand the best programming pacing mode for cardiac resynchronization therapy devices used to treat chronic heart failure.

Cardiac resynchronization therapy (CRT) efficacy trials to date used atrial-synchronous biventricular pacing wherein there is no or minimal atrial pacing. However, bradycardia and chronotropic incompetence are common in this patient population.

Despite neutral results on hard clinical outcomes of the atrial support in CRT patients, it is not clear if a rate-responsive pacing may add incremental benefits on exercise capability.

The aim of this study is to assess the impact of RR pacing compare to VVD pacing in patients implanted with CRT devices in term of functional capacity, measured by the six-minute walking test (6MWT). This simple test has shown to be an independent predictors of mortality in this cohort of patients.

Inclusion Criteria:

• Patients willing to participate in the study and signing the approved Patient Informed Consent (PIC) Form;
• Patients with approved indication for CRT by European Society of Cardiology/European Heart Rhythm Association guidelines (ESC/EHRA).
• Sinus rhythm at the time of CRT device implantation with heart rate at rest above 50 bpm.

Exclusion Criteria:

• Permanent Atrial Fibrillation;
• Inability to perform 6MWT;
• Suboptimal HF drug therapy;
• Heart rate at rest above 50 bpm.

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